"What we know so far is that these cases have involved the ingestion of blue unmarked capsules, which were purchased locally, with most believing they contained predominantly MDMA (ecstasy)," Dr Dey said.

"These cases are a further warning to people to be extremely cautious taking drugs such as these - not just at this time of the year, but all year round."

Dr Dey said people could not be sure of where drugs came from, what was in them or what effect they might have on them.

He said it was also important to avoid driving, swimming and other dangerous activities while under the influence of any drug, including alcohol.

New Year's Eve revellers who suspect a friend has overdosed are urged to call an ambulance immediately on 000.